Disclosed herein are an apparatus and a process that can be used to remove sulfur dioxide other environmentally hazardous contaminants from a gaseous waste stream while at the same time providing a source of purified water. The process can be used for the desalination of sea or brackish water, or for the concentration of contaminated waste water. The method comprises feeding a gaseous waste stream that comprises sulfur dioxide into a diffusion tower. Feed water is sprayed onto a packing material in the diffusion tower to form a thin film of feed water on a surface of the packing material. Sulfur dioxide diffuses into the thin film of feed water to form water that contains sulfur dioxide. The gaseous waste stream is simultaneously humidified. The humidified gaseous waste stream is then subjected to direct contact condensation to obtain purified water.